1. Field of the Invention
The present invention relates to an exhaust gas cleaning device of an internal combustion engine wherein a secondary-air supply passage is connected to an exhaust system of the internal combustion engine and a reed valve means is provided in the intermediate part of the secondary-air supply passage so as to be opened in response to the pulsation pressure of exhaust gas in the exhaust system in order to supply secondary air into the exhaust system and burn the unburnt components present in the exhaust system thereby to clean the exhaust gas.
2. Description of the Prior Art
Such an internal combustion engine has been already known as having a plurality of exhaust ports opened to the combustion chamber of a cylinder and exhaust pipes independent of each other communicated with these exhaust ports respectively, the exhaust pipes being made different in length from each other, thereby to improve the performance of the engine over the whole operation ranges thereof.
By the way, such an internal combustion engine has the following problem. In case of supplying secondary air for cleaning exhaust gas into the exhaust systems different in length, if the secondary-air supply passages communicated with the exhaust systems respectively are concentrated and connected to a single reed valve, which is adapted to be opened in response to the exhaust gas pulsation pressure produced in each of the exhaust systems so that secondary air is introduced into each of the exhaust systems, the exhaust gas pulsation pressures produced in the exhaust systems respectively may cancel out each other because the frequencies of the exhaust gas pulsations generated in these exhaust systems respectively differ from each other in accordance with the difference in length between the exhaust systems. Consequently, the amount of secondary air supplied to each of the exhaust systems tends to be insufficient, so that it becomes difficult to attain the expected exhaust gas cleaning effect.